The machining of precision, in particular dental, workpieces is in most cases associated with dangers for the person carrying out the machining. This is caused firstly by the machining itself and/or by the materials of the workpiece. For example, when blasting workpieces there is the danger of injury from the blasting medium itself and also by the dust that is caused by blasting, consisting of the blasting medium itself and also machined-off particles of the workpieces. In particular dental workpieces consist of materials, e.g. quartz materials, that are hazardous to health particularly in the form of small particles, e.g. dust (see danger of silicosis).
Dental workpieces are in many cases cast pieces that are cast according to models. A wax model is first made which is embedded in a moulding material which in many cases contains quartz. The wax is then melted out and liquid metal is cast into the thus gained hollow space (negative form) for which different casting methods can be used. After cooling, the moulding material must be removed. This process, described in the art as extracting or demolding is done by cracking it open with extracting or demolding means, e.g. a chisel. Particles and in particular health hazardous dust are thus necessarily freed, from which the person carrying out the machining must be protected. To ensure this, machining devices, in particular those for blasting workpieces, have been developed having a machining chamber surrounded by a housing to which a suction device can be or is connected so that particles and dust released in this way can be discharged without endangering the health of the operator. By means of a window and two sealable gripping openings for the hands, the operator has manual access to and visual contact with the machining chamber for carrying out the machining.